1. Field of the Invention
Embodiments disclosed herein may be directed to a circuit for controlling a buck-boost operation performed by one or more buck-boost converters.
2. Description of the Related Art
A buck-boost converter is a DC-DC converter that typically produces an output voltage which is either greater than or less than the input voltage. The buck-boost converter may further be seen as a switch mode power supply having a similar circuit topology from individual buck and boost converters. FIG. 1 is a diagram illustrating a conventional buck-boost converter 100. As shown in FIG. 1, buck-boost converter 100 includes a power source 102 coupled in parallel to an inductor 104, a capacitor 106, and a load 108, shown in FIG. 1 as a resistor. Buck-boost converter also includes a diode 110 and a switch 112. In operation, when switch 112 is closed, voltage source 102 is directly coupled to inductor 104 transferring current to inductor 104, resulting in the accumulation of energy in inductor 104, or the charging of inductor 104. As a result, capacitor 106 supplies current to load 108 and inductor 104 acts as a load as it charges, resulting in a lower output voltage. This lower output voltage is termed a “step-down” voltage or a “buck” voltage. When switch 112 is open, as shown in FIG. 1, inductor 104 is directly coupled to load 108 and capacitor 106, and therefore current is supplied to capacitor 106 and load 108 from inductor 104 as inductor 104 discharges, if inductor 104 has been previously charged. Inductor 104 thus acts as a current source, and provides a higher output voltage. This higher output voltage is termed a “step-up” or “boost” voltage.
Typical buck-boost converters, such as shown in FIG. 1 produce an output voltage having a polarity that is opposite to the polarity of the input voltage. In addition, the output buck voltage range may be theoretically between 0 and the input voltage, and the output boost voltage may be theoretically between the input voltage and ∞. The output voltage is adjustable based on a duty cycle of a transistor which controls switch 112.
Buck-boost converter 100 often requires complicated driving circuitry because switch 112 does not have a terminal at ground, and produces an output voltage which has a polarity opposite to the polarity of the input voltage. However, these drawbacks are minimized when voltage source 102 is a battery. As a result, buck-boost converters may often be found in battery-powered circuits to provide a variable output voltage.
Conventional buck-boost circuits, however, can not quickly be switched. Therefore, there is a need for buck-boost circuits capable of fast switching between buck and boost modes. Conventional buck-boost circuits usually buck or boost the input voltage to obtain a constant output voltage. Thus, the conventional buck-boost circuits are unidirectional. That is, the conventional buck-boost circuits buck/boost the input voltage to produce the output voltage but are not capable of bucking/boosting from the output to the input. In the case that a battery is the source of the input voltage, for example, the battery cannot be charged through the buck-boost circuit. In some cases, e.g. when the battery is a Redox battery, a wide input voltage range from the Redox battery needs to be accommodated. There is also a need for a buck-boost circuit that can be controlled externally (e.g. by a processor).